1. Field of the Invention
The instant invention relates to emergency exit door security systems, and more particularly, the instant invention relates to emergency exit door security systems wherein the system includes a time delay which delays opening of an emergency exit door for a predetermined interval, as long as there is no emergency condition. Upon the occurrence of an emergency condition, the door unlocks immediately.
2. Technical Considerations and Prior Art
As is set forth in the aforecited U.S. patent applications, there is a need for a new type of emergency exit door lock or latch which delays opening of an emergency exit door. In these patent applications, delay is accomplished by either throttling a fluid while an attempt is being made to open the door; by initiating an electrical delay of a release mechanism after an attempt has been made to open the door, or by a combination of both the hydraulic and electrical delays. In each device disclosed in these patent applications, an emergency release is provided which allows the latches to release immediately upon the occurrence of an emergency situation. For example, the latches are connected to smoke detectors and pull boxes which, when activated, permit the latches to bypass any restraint on their opening. Moreover, when there is an interruption of electric current to these latches, the latches will allow the doors to open when pushed.
In order to successfully commercialize the concepts disclosed in the aforecited patent applications, it was deemed advisable to simplify the latching mechanism so that the mechanism could be assembled from relatively inexpensive, stamped parts and from off-the-shelf, purchased parts. Moreover, the hydraulic circuits necessitated by utilizing solenoid-operated valves in conjunction with hydraulic cylinders made the arrangements disclosed in these patent applications expensive while compromising reliability. In a system which has both a hydraulic delay and electronic delay, the electronic delay should ideally be completely independent of the hydraulic delay. However, in the systems disclosed in the aforecited patent applications, the electronic delay functions within the hydraulic system by opening a valve which lets hydraulic fluid bypass a throttle. Thus the two systems are not completely independent which compromises the device's redundancy.
As is set forth in parent application Ser. No. 148,383, filed May 9, 1980, now U.S. Pat. No. 4,354,699 in the name of Emanuel L. Logan Jr., under certain circumstances it may be desirable to divorce the unlatching structure of a door, such as an emergency exit door, from the delay structure, so that the delay structure can be retrofitted on existing doors which already have their own hardware. Such an approach is disclosed in U.S. Pat. No. 4,257,631 entitled "Magnetic Emergency Exit Door Lock With Delayed Opening" and in copending patent application Ser. No. 089,398, now U.S. Pat. No. 4,314,722, entitled "Timing Apparatus For Delaying Opening Of Doors". Both of these approaches have disadvantages which may forestall their use. With a magnetic arrangement, there is a problem of residual magnetism which must be overcome in order to open a door even after the magnet is de-energized. In the door closure type of delay device, the door is never completely free of the door closure jamb, which can interfere with ordinary operation of the door when the door operates in a non-delay mode. Accordingly, there is a need for a delay apparatus which can be easily applied to emergency exit doors as a retrofit for existing installations or as an accessory for planned installations which also use conventional latching and locking hardware.
As is apparent from the above discussions, it is desirable to both improve the locking or latching mechanism from the standpoint of both reliability and cost, and it is desirable to provide a delay mechanism which both operates effectively and can be retrofitted to existing exit doors.